Jupiter's Moon Ganymede - Universe Today Universe Today by Matt Williams In 1610, Galileo Galilei looked up at the night sky through a telescope of his own design . Spotting Jupiter, he noted the presence of several “luminous objects” surrounding it, which he initially took for stars. In time, he would notice that these “stars” were orbiting the planet, and realized that they were in fact Jupiter’s moons – which would come to be named Io , Europa , Ganymede and Callisto . Of these, Ganymede is the largest, and boasts many fascinating characteristics. In addition to being the largest moon in the Solar System, it is also larger than even the planet Mercury. It is the only satellite in the Solar System known to possess a magnetosphere, has a thin oxygen atmosphere, and (much like its fellow-moons, Europa and Callisto) is believed to have an interior ocean.

Discovery and Naming: Though Chinese astronomical records claim that astronomer Gan De may have spotted a moon of Jupiter (probably Ganymede) with the naked eye as early as 365 BCE, Galileo Galilei is credited with making the first recorded observation of Ganymede on January 7th, 1610 using his telescope. Together with Io, Europa and Callisto, he named them the “Medicean Stars” at the time – after his patron, the Grand Duke of Tuscany, Cosimo de’ Medici. Simon Marius, a German astronomer and contemporary of Galileo’s who claimed to have independently discovered Ganymede, suggested alternative names at the behest of Johannes Kepler. However, the names of Io, Europa, Ganymede and Callisto – which were all taken from classical mythology – would not come to formally be adopted until the 20th century. Illustration of Jupiter and the Galilean satellites. Credit: NASA Prior to this, the Galilean Moons were named Jupiter I through IV based on their proximity to the planet (with Ganymede designated as Jupiter III).

Following the discovery of the moons of Saturn, a naming system based on that of Kepler and Marius was used for Jupiter’s moons. In Greek mythology, Ganymede was the son of King Tros (aka. Ilion), the namesake of the city of Troy (Ilium). Size, Mass and Orbit: With a mean radius of 2634.1 ± 0.3 kilometers (the equivalent of 0.413 Earths), Ganymede is the largest moon in the Solar System and is even larger than the planet Mercury. However, with a mass of 1.4819 x 10²³ kg (the equivalent of 0.025 Earths), it is only half as massive. This is due to Ganymede’s composition, which consists of water ice and silicate rock (see below). Ganymede’s orbit has a minor eccentricity of 0.0013, with an average distance (semi-major axis) of 1,070,400 km – varying from 1,069,200 km at periapsis to at 1,071,600 km apoapsis.

Ganymede takes seven days and three hours to completes a single revolution. Like most known moons, Ganymede is tidally locked, with one side always facing toward the planet. Its orbit is inclined to the Jovian equator, with the eccentricity and inclination changing quasi-periodically due to solar and planetary gravitational perturbations on a timescale of centuries. These orbital variations cause the axial tilt to vary between 0 and 0.33°. Ganymede has a 4:1 orbital resonance with Io and a 2:1 resonance with Europa. Ganymede is the largest satellite in our solar system, larger than Mercury and Pluto, and three-quarters the size of Mars. Credit: NASA/JPL Essentially, this means that Io orbits Jupiter four times (and Europa twice) for every orbit made by Ganymede. The superior conjunction between Io and Europa occurs when Io is at periapsis and Europa is at apoapsis, and the superior conjunction between Europa and Ganymede occurs when Europa is at periapsis. Such a complicated resonance (a 4:2:1 resonance) is called the Laplace Resonance .

Composition and Surface Features: With an average density of 1.936 g/cm3, Ganymede is most likely composed of equal parts rocky material and water ice. It is estimated that water ice constitutes 46–50% of the moon’s mass (slightly lower than that of Callisto) with the possibility of some additional volatile ices such as ammonia being present. Ganymede’s surface has an albedo of about 43%, which suggests that water ice makes up a mass fraction of 50-90% the surface. Near-infrared and ultra-violet surveys have also revealed the presence of carbon dioxide, sulfur dioxide, and possibly cyanogen, hydrogen sulfate and various organic compounds. More recent data has shown evidence of salts such as magnesium sulfate and possibly sodium sulfate, which may have originated from the subterranean ocean (see below). Ganymede’s interior appears to be fully differentiated, consisting of a solid inner core made of iron, a liquid iron and iron-sulfide outer core, a silicate mantle, and a a spherical shell of mostly ice surrounding the rock shell and the core.

The core is believed to measure 500 km in radius, and has a temperature of about 1500 – 1700 K and pressure of up to 10 GPa. Artist’s cut-away representation of the internal structure of Ganymede, with layers shown to scale. Credit: Wikipedia Commons/kelvinsong The most compelling evidence for the existence of a liquid, iron-nickel-rich core is Ganymede’s intrinsic magnetic field. The convection in the liquid iron, which has high electrical conductivity, is the most reasonable model of magnetic field generation.The density of the core is believed to be 5.5 – 6 g/cm³, while the silicate mantle has an estimated density of 3.4 – 3.6 g/cm³. This mantle is composed of silicate materials, most likely chondrites and iron. The outer ice shell is the largest layer of all, measuring an estimated 800 km (497 miles) thick. The precise thicknesses of this and other layers in the interior of Ganymede depends on the assumed composition of silicates and amount of sulfur in the core.

Scientists also believe that Ganymede has a thick ocean nestled between two layers of ice – a tetragonal layer between it and the core and a hexagonal layer above it. The presence of this ocean has been confirmed by readings taken by orbiters and through studies of how Ganymede’s aurora behaves. In short, the moon’s auroras are affected by Ganymede’s magnetic field, which in turn is affected by the presence of a large, subsurface salt-water ocean. Ganymede’s surface is a mix of two types of terrain. There’s the very old, highly cratered, and dark regions, and the somewhat younger, lighter regions marked with an extensive array of grooves and ridges. In a way that is similar to Europa, Ganymede’s surface is asymmetric, with the leading hemisphere being brighter than the trailing one. The dark terrain, which comprises about one-third of the surface, is so-colored because the surface ice in these regions contains clays and organic materials. It has been theorized that these have been left behind by impactors, which accords with the fact that impact craters are far more extensive in the areas of dark terrain.

Meanwhile, the grooved terrain is believed to be tectonic in nature; which could be due in part to cryovolcanism , but is thought to be mostly the result of tidal heating events. The tidal flexing could have heated the interior and strained the lithosphere, leading to the development of cracks, graben and faults that erased the old, dark terrain on 70% of the surface. Though craters are more common in the darker areas, they are seen all over the surface. Ganymede may have experienced a period of heavy cratering 3.5 to 4 billion years ago similar to that of the Moon. If true, the vast majority of impacts happened in that epoch, whereas the cratering rate has been much smaller since. Craters on Ganymede are also flatter than those on the Moon and Mercury, which is probably due to the relatively weak nature of Ganymede’s icy crust. Ganymede also has polar caps, likely composed of water frost, which were first seen by the Voyager spacecraft. Since the discovery, several theories have been proposed for their formation, ranging from the thermal migration of water vapor to higher latitudes to plasma bombardment turning the ice brighter.

Data obtained by the Galileo spacecraft – which noted a very close correspondence between the polar cap boundary and the boundaries of the moon’s magnetic field – suggests that the latter theory is correct. Atmosphere: Similar to Europa, Ganymede has a tenuous oxygen atmosphere. Also similar to Europa is how the atmosphere formed, which involves water ice on the surface being split into hydrogen and oxygen through interaction with UV radiation, the hydrogen being lost to space and the oxygen being retained. The surface pressure of this atmosphere is thought to lie within the range of 0.2–1.2 micro Pascals. Montage showing New Horizons’ views of Ganymede taken by it’s infrared spectrometer and LORRI and LEISA instruments. Credit: NASA/Johns Hopkins University APL/SwRI The presence of this atmosphere also causes an airglow effect, a faint emission of light caused by the interaction of atomic oxygen and energetic particles. This effect is not uniformly distributed (as with Europa), but instead causes bright spots to appear above the polar regions – which could be “polar auroras” – due to the planet’s magnetic field. Additional evidence of the oxygen atmosphere comes from the detection of various gases trapped in the ice on Ganymede.

This evidence consisted of the spectroscopic detection of ozone (O³), as well as absorption features that indicated the presence of oxygen gas (O²). Another constituent of the atmosphere is hydrogen, which (despite most being lost to space) still exists at a surface in very minor concentrations. The existence of this neutral atmosphere implies that an ionosphere should exist since oxygen molecules are ionized by the impacts of the energetic electrons coming from the magnetosphere and by solar electromagnetic UV radiation. However, the existence of an ionosphere remains controversial, due to conflicting data gathered by different missions. Magnetosphere: Ganymede is unique among moons in the Solar Systems in that it alone has a magnetosphere. The value of the moon’s permanent magnetic moment is estimated to be 1.3 x 10¹³ T·m³, which is three times larger than the magnetic moment of Mercury. The magnetic dipole is tilted with respect to the rotational axis of Ganymede by 176°, which means that it is directed against the Jovian magnetic moment. The magnetic field of Jupiter and co-rotation enforcing currents.

Credit: Wikipedia Commons/Ruslik0 The dipole magnetic field created by this permanent moment has a strength of 719 ± 2 Teslas (nT) at Ganymede’s equator, and roughly twice that at the poles (1440 nT). This magnetic moment also carves a part of space around Ganymede, creating a tiny magnetosphere embedded inside that of Jupiter with a diameter of about 10,525 – 13,156 km. The Ganymedian magnetosphere has a region of closed field lines located below 30° latitude, where charged particles (electrons and ions) are trapped, creating a kind of radiation belt. The main ion species in the magnetosphere is single ionized oxygen, which fits well with Ganymede’s tenuous oxygen atmosphere. The interaction between the Ganymedian magnetosphere and Jovian plasma is in many respects similar to that of the solar wind and Earth’s magnetosphere. The plasma co-rotating with Jupiter impinges on the trailing side of the Ganymedian magnetosphere much like the solar wind impinges on the Earth’s magnetosphere.

In addition to the intrinsic magnetic moment, Ganymede has an induced dipole magnetic field who’s existence is connected with the variation of the Jovian magnetic field near Ganymede. The induced magnetic field of Ganymede is similar to those of Callisto and Europa, indicating that this moon also has a subsurface water ocean with a high electrical conductivity. Artist’s concept of aurorae on Ganymede. Credit: NASA/ESA However, the existence of Ganymede’s magnetosphere remains a bit of a mystery. On the one hand, its existence is believed to be the result of Ganymede’s a dynamo effect caused by conducting material moving in the core, similar to Earth. However, other bodies that have differentiated metallic cores don’t have magnetospheres, and the relatively small size of Ganymede’s core suggests that it should have cooled sufficiently that fluid motions are no longer possible. One explanation for this incongruity is that the same orbital resonances that may have disrupted the surface also allow the magnetic field to persist. With tidal heating increasing during such resonances, the mantle may have insulated the core, preventing it from cooling.

Another explanation is a remnant magnetization of silicate rocks in the mantle, which is possible if the satellite had a more significant dynamo-generated field in the past. Habitability: There is some speculation on the potential habitability of Ganymede’s ocean. An analysis published in 2014 , taking into account the realistic thermodynamics for water and effects of salt, suggests that Ganymede might have a stack of several ocean layers separated by different phases of ice, with the lowest liquid layer adjacent to the rocky mantle below. This is important, since the layer closest to the rocky interior would be subject to heating due to tidal flexing in the mantle. This heat could be transferred into the water via hydrothermal vents , which could provide the necessary heat and energy to sustain life. Combined with oxygenated water, life forms could exist at the core-mantle boundary in the form of extremophiles, in a way that is similar to what is found in Earth’s oceans (and presumed to exist in Europa’s interior ocean).

Exploration: Several probes flying by or orbiting Jupiter have explored Ganymede more closely, including four flybys in the 1970s, and multiple passes in the 1990s to 2000s. The first approaches were conducted by the Pioneer 10 and 11 probes, which approached the moon in 1973 and 1974, respectively. These missions returned more specific information on its physical characteristics and resolved features to 400 km (250 mi) on its surface. The next missions came in 1979, when the Voyager 1 and 2 probes passed the moon, refining estimates of its size and revealing its grooved terrain for the first time. In 1995, the Galileo spacecraft orbited Jupiter and went on to make six close flybys between 1996 and 2000. The probe’s findings included the discovery of Ganymede’s magnetic field, the moon’s interior ocean, and a large number of spectral images that showed non-ice compounds on the surface. Artist impression of New Horizons conducting its flyby of Jupiter.

Image credit: NASA/JPL/JHUAPL The most recent mission to Ganymede was made by the New Horizons probe in 2007. While en route to Pluto, the probe obtained topographic and composition mapping data of Europa and Ganymede during its flyby of Jupiter. Their are no missions to Ganymede currently in operation, but several missions have been proposed for the coming decades. One such proposal is the joint NASA/ESA Europa Jupiter System Mission (EJSM), which would explore Jupiter’s moons (including Ganymede) and has a proposed launch date of 2020. The mission would consist of NASA’s Jupiter Europa Orbiter, the ESA’s Jupiter Ganymede Orbiter, and possibly a JAXA Jupiter Magnetospheric Orbiter. The ESA’s contribution was renamed the Jupiter Icy Moon Explorer (JUICE) in 2012, and obtained a launch slot aboard the ESA’s Cosmic Vision science program (scheduled for launch in 2022 or 2024).

This may include a partner mission from the Russian Space Research Institute – known as the Ganymede Lander (GL) – and would involve JUICE examining Ganymede from orbit and conducting multiple flybys or Europa and Callisto. A Ganymede orbiter based on the Juno probe was also proposed in 2010 for the Planetary Science Decadal Survey. As part of the committee report presented at the Survey – titled “ Vision and Voyagers for Planetary Science in the Decade 2013-2022 ” – a concept study for a possible Ganymede Orbiter was proposed, which included recommendations on instrumentation. Artist’s concept of the Jupiter Icy Moons Orbiter (JIMO), a cancelled program that envisioned sending a spacecraft to inspect Callisto, Ganymede and Europa. Credit: NASA/JPL A canceled proposal for a Ganymede orbiter was the Jupiter Icy Moons Orbiter (JIMO), which would have performed a flyby of Europa, Ganymede and Callisto. Designed to use nuclear fission for power and an ion engine for propulsion, JIMO would have studied Ganymede in greater detail than an previous orbiter.

However, the mission was canceled in 2005 because of budget cuts. Colonization: Ganymede is considered a possible candidate for human settlement – and even terraforming – due to the many advantages it presents. For one, as Jupiter’s largest moon, Ganymede has a gravitational force of 1.428 m/s2 (the equivalent of 0.146 g) which is comparable to Earth’s Moon. Sufficient enough to limit the effects of muscle and bone degeneration, this lower gravity also means that the moon has a lower escape velocity – which means it would take considerably less fuel for rockets to take off from the surface. What’s more, the presence of a magnetosphere means that colonists would be better shielded from cosmic radiation than on other bodies. The prevalence of water ice means that colonists could also produce breathable oxygen, their own drinking water, and would be able to synthesize rocket fuel. Unfortunately, beyond this, Ganymede presents numerous challenges for colonization. For starters, the presence of a magnetosphere does not shield Ganymede from enough cosmic radiation to ensure human safety, due to the fact that it is overshadowed by Jupiter’s powerful magnetic field.

This results in the surface receiving some 8 rem of radiation per day – which is 333 times the average of what Earth-bound organisms experience in a year. Artist’s concept for a future settlement on Ganymede. Credit: futuretimeline.net The dominance of Jupiter’s magnetic field also means that Ganymede’s magnetosphere is not strong enough to retain an atmosphere of sufficient density to sustain human beings. It would also be insufficient to retain much heat. Hence, settlements on the surface would need to be heavily insulated, shielded from radiation, and contain a breathable atmosphere. A possible solution to this, similar to what has been proposed for Europa, would be for colonists to build settlements within the icy mantle, or possibly under the surface of the ice entirely. These embedded (or aquatic habitats) would be shielded from harmful cosmic radiation by the icy mantle. They could also function as conduits between the ocean and the surface, piping water in and processing it into fuel for export. However, such possibilities are still far from realization and in the meantime, exploring Ganymede and deciphering its deeper mysteries remains the priority. And of these, Ganymede has several!

Much like the other Galilean moons, Ganymede possesses a wealth of unique and mysterious attributes, many of which still defy comprehension. In addition to being the largest moon in the Solar System, it is the only moon other than Earth (and the gas giants) to have a magnetic field. And of course, there’s the possibility that life could exist beneath its icy crust, possibly in microbial or extreme form. All of these make Ganymede an intriguing prospect for future exploration. We have many interesting articles on Ganymede and Jupiter’s Moons here at Universe Today. Here is a list of the Galilean Moons , as well as Jupiter’s entire system of moons . Here is one about Ganymede’s interior ocean , and how an amateur astronomer made a detailed map of Ganymede . Here’s a list of all the largest moons in the Solar System, and a listing of the largest moons and smallest planets at Solar Views. Universe Today has whole series of podcasts about the Solar System at Astronomy Cast .

Share this: Ganymede, biggest moon in the solar system, has a saltwater ocean - CNET CNET Ganymede, biggest moon in the solar system, has a saltwater ocean Ganymede, biggest moon in the solar system, has a saltwater ocean NASA says new observations from the Hubble Space Telescope confirm the presence of a subsurface ocean on Jupiter's largest moon. Up Next Obama retaliates against Russia over election hacking This artist's concept shows Ganymede in the shadow of Jupiter, with its aurorae glowing.Photo by NASA/ESA NASA says new observations from the Hubble Space Telescope confirm the existence of a salty subsurface ocean on Ganymede , the largest moon in the solar system, which orbits our largest neighbor planet, Jupiter. The ocean is estimated to be about 60 miles thick -- 10 times deeper than the Mariana Trench, the deepest part of the Pacific -- but is buried under a layer of mostly icy crust 95 miles thick. Ganymede joins other neighborhood moons like Europa, the asteroid belt dwarf planet Ceres , and Saturn's Enceladus and Titan that host strange icy or liquid layers, making them prime targets in the search for life beyond Earth.

Scientists have hypothesized for decades that Ganymede might harbor an icy or even liquid ocean beneath its frigid surface. The key to confirming the presence of a saltwater ocean came from observing Ganymede's aurorae, which would look bright red to a human able to stand on the surface of the moon and gaze up through its thin oxygen atmosphere. But don't get too excited, it's much too thin to support life as we know it. 7 Jupiter's Ganymede moon hides a big ocean (pictures) Auroral phenomena -- think the bright northern lights of the aurora borealis or the aurora australis down south -- are not fully understood, but are linked to magnetic fields interacting with the solar wind. Ganymede is the only moon in the solar system that generates its own magnetic field thanks to its liquid iron core, but it also lies within the magnetic field of massive Jupiter. As Jupiter's magnetic field changes, it affects the aurorae on Ganymede, causing them to "rock back and forth" according to Joachim Saur, a professor for geophysics at the University of Cologne, who presented the news on a NASA teleconference Thursday.

Related stories See the submarine NASA wants to send to Saturn's moon Titan Saur explained that the rocking effect seemed to be dampened by something else. Rather than altering the aurorae six degrees, as models suggested that they should given the electromagnetic fields involved, they only changed by two degrees, leading scientists to conclude that the rocking is inhibited by a salty subsurface ocean. "This confirms the existence of an ocean and simultaneously rules out the absence of an ocean," he told reporters. 9 more habitable planets found A NASA discovery means there are a lot more planets that may be able to support life. Also, Amazon takes on YouTube. Get all caught up in tech right here. by Iyaz Akhtar Close Drag The news comes on the heels of the finding earlier this week that Saturn's moon Enceladus may contain enough warm water to support life. Ganymede will also now be more competitive when it comes to garnering attention among the Jovian moons -- its sibling Europa and its presumed subsurface ocean has long excited space geeks, even working its way into the priority list for future NASA missions. Looks like NASA may now need to add another moon to its itinerary for that deep-space journey.

Solar System’s Largest Moon Has a Saltwater Ocean Greater Than All the Water on Earth - IGN IGN Solar System’s Largest Moon Has a Saltwater Ocean Greater Than All the Water on Earth Share Jupiter's Largest Moon Has an Ocean with More Water Than Earth Jupiter's Largest Moon Has an Ocean with More Water Than Earth Scientists Say the Warm Oceans of Enceladus May Harbour Lifeforms NASA Reveals Mars May Once Have Had a Massive Ocean Next 13 Mar 2015 Solar System’s Largest Moon Has a Saltwater Ocean Greater Than All the Water on Earth Share. By Jenna Pitcher Jupiter’s largest moon Ganymede may have a subterranean saltwater ocean that is thought to have more water than all the water on Earth's surface. The underground body of water is estimated to be 60 miles (100 km) deep, up to 10 times deeper than Earth's oceans , and lays under a 95-mile (150 km) shell of ice and rock. “This discovery marks a significant milestone, highlighting what only Hubble can accomplish,” said John Grunsfeld, associate administrator of NASA’s Science Mission Directorate, in a prepared statement. Got feedback on our player? We want to hear it.

“In its 25 years in orbit, Hubble has made many scientific discoveries in our own solar system," Grunsfeld adds. "A deep ocean under the icy crust of Ganymede opens up further exciting possibilities for life beyond Earth.” Ganymede, the largest moon in our solar system, is the only satellite with its own magnetic field. Its field generates aurorae that “rocks back and forth” when Jupiter’s own magnetic field changes. Using NASA’s Hubble Space Telescope, a team of scientists at the University of Cologne monitored Ganymede's auroral belts and found that the amount of rocking in the magnetic field suggests that the moon has a subsurface saltwater ocean. Got feedback on our player? We want to hear it. "I was always brainstorming how we could use a telescope in other ways," project lead Joachim Saur, project lead, in a prepared statement. "Is there a way you could use a telescope to look inside a planetary body? Then I thought, the aurorae! Because aurorae are controlled by the magnetic field, if you observe the aurorae in an appropriate way, you learn something about the magnetic field.

If you know the magnetic field, then you know something about the moon’s interior." The news follows a reveal by scientists earlier this week that Saturn’s sixth-largest moon Enceladus is now believed to the most habitable body ever discovered outside of Earth . The ice moon’s south pole resemble deep oceans on Earth with a heated ocean exhibiting ongoing hydrothermal activity. NASA scientists also recently discovered that Mars may once have had a massive ocean covering half of its northern hemisphere. Jenna Pitcher is a freelance journalist writing for IGN. You can follow her on Twitter . IGN Recommends Largest solar system moon detailed in geologic map | Astronomy.com Largest solar system moon detailed in geologic map Largest solar system moon detailed in geologic map The map of Ganymede combines the best images obtained during flybys conducted by NASA’s Voyager 1 and 2 spacecraft and Galileo orbiter. To present the best information in a single view of Jupiter's moon Ganymede, a global image mosaic was assembled, incorporating the best available imagery from NASA's Voyager 1 and 2 spacecraft and NASA's Galileo spacecraft.

USGS Astrogeology Science Center/Wheaton/NASA/JPL-Caltech More than 400 years after its discovery by astronomer Galileo Galilei, the largest moon in the solar system — Jupiter’s moon Ganymede — has finally claimed a spot on the map. A group of scientists led by Geoffrey Collins of Wheaton College in Massachusetts has produced the first global geologic map of Ganymede, Jupiter’s seventh moon. The map combines the best images obtained during flybys conducted by NASA’s Voyager 1 and 2 spacecraft (1979) and Galileo orbiter (1995 to 2003) and is now published by the U. S. Geological Survey as a global map. It technically illustrates the varied geologic character of Ganymede’s surface and is the first global geologic map of this icy outer-planet moon. “This map illustrates the incredible variety of geological features on Ganymede and helps to make order from the apparent chaos of its complex surface,” said Robert Pappalardo of NASA’s Jet Propulsion Laboratory in Pasadena, California.

“This map is helping planetary scientists to decipher the evolution of this icy world and will aid in upcoming spacecraft observations.” The European Space Agency’s Jupiter Icy Moons Explorer mission is slated to be orbiting Ganymede around 2032. NASA is contributing a U.S.-led instrument and hardware for two European-led instruments for the mission. Since its discovery in January 1610, Ganymede has been the focus of repeated observation, first by Earth-based telescopes, and later by the flyby missions and spacecraft orbiting Jupiter. These studies depict a complex icy world whose surface is characterized by the striking contrast between its two major terrain types: the dark, very old, highly cratered regions and the lighter, somewhat younger — but still very old — regions marked with an extensive array of grooves and ridges. According to the scientists who have constructed this map, three major geologic periods have been identified for Ganymede that involve the dominance of impact cratering, then tectonic upheaval, followed by a decline in geologic activity.

The map, which illustrates surface features, such as furrows, grooves, and impact craters, allows scientists to decipher distinct geologic time periods for an object in the outer solar system for the first time. “The highly detailed colorful map confirmed a number of outstanding scientific hypotheses regarding Ganymede’s geologic history and also disproved others,” said Baerbel Lucchitta of the U.S. Geological Survey in Flagstaff, Arizona, who has been involved with geologic mapping of Ganymede since 1980. “For example, the more detailed Galileo images showed that cryovolcanism, or the creation of volcanoes that erupt water and ice, is very rare on Ganymede.” The Ganymede global geologic map will enable researchers to compare the geologic characters of other icy satellite moons because almost any type of feature that is found on other icy satellites has a similar feature somewhere on Ganymede. “The surface of Ganymede is more than half as large as all the land area on Earth, so there is a wide diversity of locations to choose from,” Collins said.

“Ganymede also shows features that are ancient alongside much more recently formed features, adding historical diversity in addition to geographic diversity.” 0 Read and share your comments on this article RELATED ARTICLES What is the largest moon in the Solar System? | Cool Cosmos What is the largest moon in the Solar System? One of Jupiter's moons, Ganymede, is the largest moon in the Solar System. Ganymede has a diameter of 3270 miles (5,268 km) and is larger than the planet Mercury. It has a rocky core with a water/ice mantle and a crust of rock and ice. Ganymede has mountains, valleys, craters and old lava flows. Continue the conversation on Planets For Kids - Solar System Facts and Astronomy Read More IO Jupiter is the largest planet in the Solar System and has at least 16 large moons and even more very small ones. Four of Jupiter’s Read More Phobos Mars has two moons. The first of these moons is Phobos, named for a character in the legendary piece of Greek literature, The Iliad.

Phobos was discovered in 1877 by Asaph Hall and at first glance looks very little like our moon we see every night above the trees. Read More Deimos Deimos ( Dee-Mos) is the second of two moons orbiting Mars. It is considered the second moon because it is much farther away from Mars than the first moon, Phobos. It is still a bit strange compared to our Moon which is generally round and follows a set pattern around the Earth. Deimos... Read More Europa The planet Jupiter is the largest planet in the Solar System and has a huge number of moons that orbit around it. Read More Ganymede Ganymede is one of the many satellites, or moons, that orbit round the great planet, Jupiter. None of these moons can be seen with the naked eye but the four... Read More Callisto Jupiter is the giant of the Solar System and has something like 50 or more satellites. A satellite is something that orbits around a body in space. Planet Jupiter: Facts About Its Size, Moons and Red Spot Planet Jupiter: Facts About Its Size, Moons and Red Spot By Charles Q.

Choi, Space.com Contributor | November 14, 2014 12:59am ET MORE This photo of Jupiter was taken on Sept. 20, 2010 when Jupiter made its closest approach to Earth since 1963. (Uranus [insert] was visible through telescopes near Jupiter.) Credit: Jimmy Eubanks Jupiter is the largest planet in the solar system. Fittingly, it was named after the king of the gods in Roman mythology. In a similar manner, the ancient Greeks named the planet after Zeus, the king of the Greek pantheon. Jupiter helped revolutionize the way we saw the universe and ourselves in 1610, when Galileo discovered Jupiter's four large moons — Io, Europa, Ganymede and Callisto, now known as the Galilean moons. This was the first time celestial bodies were seen circling an object other than Earth, major support of the Copernican view that Earth was not the center of the universe.

Physical characteristics Jupiter is the most massive planet in our solar system , more than twice as massive as all the other planets combined, and had it been about 80 times more massive, it would have actually become a star instead of a planet. Its atmosphere resembles that of the sun, made up mostly of hydrogen and helium, and with four large moons and many smaller moons in orbit around it, Jupiter by itself forms a kind of miniature solar system. All told, the immense volume of Jupiter could hold more than 1,300 Earths. The colorful bands of Jupiter are arranged in dark belts and light zones created by strong east-west winds in the planet's upper atmosphere traveling more than 400 mph (640 kph). The white clouds in the zones are made of crystals of frozen ammonia, while darker clouds of other chemicals are found in the belts. At the deepest visible levels are blue clouds. Far from being static, the stripes of clouds change over time . Inside the atmosphere, diamond rain may fill the skies. The most extraordinary feature on Jupiter is undoubtedly the Great Red Spot , a giant hurricane-like storm seen for more than 300 years.

At its widest, the Great Red Spot is three times the diameter of the Earth, and its edge spins counterclockwise around its center at a speed of about 225 mph (360 kph). The color of the storm, which usually varies from brick red to slightly brown, may come from small amounts of sulfur and phosphorus in the ammonia crystals in Jupiter's clouds. The spot grows and shrinks over time, and every now and again, seems to fade entirely. Jupiter's gargantuan magnetic field is the strongest of all the planets in the solar system at nearly 20,000 times the strength of Earth's. It traps electrically charged particles in an intense belt of electrons and other electrically charged particles that regularly blasts the planet's moons and rings with a level of radiation more than 1,000 times the lethal level for a human, damaging even heavily shielded spacecraft such as NASA's Galileo probe.

The magnetosphere of Jupiter, which is composed of these fields and particles, swells out some 600,000 to 2 million miles (1 million to 3 million km) toward the sun and tapers to a tail extending more than 600 million miles (1 billion km) behind Jupiter. Jupiter spins faster than any other planet, taking a little under 10 hours to complete a turn on its axis, compared with 24 hours for Earth. This rapid spin makes Jupiter bulge at the equator and flatten at the poles, making the planet about 7 percent wider at the equator than at the poles. Jupiter broadcasts radio waves strong enough to detect on Earth. These come in two forms — strong bursts that occur when Io, the closest of Jupiter's large moons, passes through certain regions of Jupiter's magnetic field, and continuous radiation from Jupiter's surface and high-energy particles in its radiation belts. These radio waves could help scientists to probe the oceans on its moons.

Composition & structure Atmospheric composition (by volume): 89.8 percent molecular hydrogen, 10.2 percent helium, minor amounts of methane, ammonia, hydrogen deuteride, ethane, water, ammonia ice aerosols, water ice aerosols, ammonia hydrosulfide aerosols Magnetic field: Nearly 20,000 times stronger than Earth's Chemical composition: Jupiter has a dense core of uncertain composition , surrounded by a helium-rich layer of fluid metallic hydrogen, wrapped up in an atmosphere primarily made of molecular hydrogen. Internal structure: A core less than 10 times Earth's mass surrounded by a layer of fluid metallic hydrogen extending out to 80 to 90 percent of the diameter of the planet, enclosed in an atmosphere mostly made of gaseous and liquid hydrogen. Orbit & rotation Average distance from the sun : 483,682,810 miles (778,412,020 km). By comparison: 5.203 times that of Earth Perihelion (closest approach to the sun): 460,276,100 miles (740,742,600 km).

By comparison: 5.036 times that of Earth Aphelion (farthest distance from the sun): 507,089,500 miles (816,081,400 km). By comparison: 5.366 times that of Earth (Source: NASA .) Jupiter's moons Jupiter has at least 63 moons , which are often named after the Roman god's many lovers. The four largest moons of Jupiter, now called Io, Europa, Ganymede, and Callisto, were discovered by Galileo Galilei himself, and are appropriately known today as the Galilean satellites. Ganymede is the largest moon in our solar system, larger even than Mercury and Pluto. It is also the only moon known to have its own magnetic field. The moon has at least one thick ocean between layers of ice, although it may contain several layers of both materials. Io is the most volcanically active body in our solar system. The sulfur its volcanoes spew out gives Io a blotted yellow-orange appearance that is often compared to a pepperoni pizza.

As Io orbits Jupiter, the planet's immense gravity causes 'tides' in Io's solid surface that rise 300 feet (100 meters) high, generating enough heat for volcanic activity. The frozen crust of Europa is made up mostly of water ice, and it may hide a liquid ocean holding twice as much water as Earth does. Icy oceans may also exist beneath the crusts of Callisto and Ganymede. Some of this liquid spouts from the surface in newly spotted sporadic plumes at the southern pole. Its potential to host life caused NASA to request funding for a mission to explore Europa . Callisto has the lowest reflectivity, or albedo, of the four Galilean moons. This suggests that its surface may be composed of dark, colorless rock. Jupiter's rings Jupiter's three rings came as a surprise when NASA's Voyager 1 spacecraft discovered them around the planet's equator in 1979. Each are much fainter than Saturn's rings. The main ring is flattened. It is about 20 miles (30 km) thick and more than 4,000 miles (6,400 km) wide.

The inner cloud-like ring, called the halo, is roughly 12,000 miles (20,000 km) thick. The halo extends halfway from the main ring down to the planet's cloud tops and expands by interaction with Jupiter's magnetic field. Both the main ring and halo are composed of small, dark particles. The third ring, known as the gossamer ring because of its transparency, is actually three rings of microscopic debris from three of Jupiter's moons, Amalthea, Thebe and Adrastea. It is probably made up of dust particles less than 10 microns in diameter, about the same size of the particles found in cigarette smoke, and extends to an outer edge of about 80,000 miles (129,000 km) from the center of the planet and inward to about 18,600 miles (30,000 km). Ripples in the rings of both Jupiter and Saturn may be signs of impacts from comets and asteroids.

Research & exploration Seven missions have flown by Jupiter — Pioneer 10 , Pioneer 11 , Voyager 1 , Voyager 2 , Ulysses, Cassini and New Horizons — while another, NASA's Galileo, actually orbited the planet. Pioneer 10 revealed how dangerous Jupiter's radiation belt is, while Pioneer 11 provided data on the Great Red Spot and close-up pictures of its polar region. Voyager 1 and 2 helped astronomers create the first detailed maps of the Galilean satellites, discovered Jupiter's rings, revealed sulfur volcanoes on Io, and saw lightning in Jupiter's clouds. Ulysses discovered the solar wind has a much greater impact on Jupiter's magnetosphere than before suggested. New Horizons took close-up pictures of Jupiter and its largest moons. In 1995, Galileo sent a probe plunging towards Jupiter, making the first direct measurements of its atmosphere and measuring the amount of water and other chemicals there. When Galileo ran low on fuel, the craft was intentionally crashed into Jupiter's atmosphere to avoid any risk of it slamming into and contaminating Europa, which might have an ocean below its surface capable of supporting life.

Another spacecraft, named Juno , is heading toward Jupiter and will reach the planet in 2016. It will study Jupiter from a polar orbit to figure out how it and the rest of the solar system formed, which could shed light on how alien planetary systems might have developed. Jupiter's gravitational impact on the solar system As the most massive body in the solar system after the sun, the pull of Jupiter's gravity has helped shape the fate of our system. It may have violently hurled Neptune and Uranus outward , according to calculations published in the journal Nature. Jupiter, along with Saturn, may have slung a barrage of debris toward the inner planets early in the system's history, according to an article in Science magazine. It may even nowadays help keep asteroids from bombarding Earth, and recent events certainly have shown that it can absorb potentially deadly impacts . Currently, Jupiter's gravitational field influences numerous asteroids that have clustered into the regions preceding and following Jupiter in its orbit around the sun. These are known as the Trojan asteroids, after three large asteroids there, Agamemnon, Achilles and Hector, names drawn from the Iliad, Homer's epic about the Trojan War.

Possibility of life on Jupiter If one were to dive into Jupiter's atmosphere , one would discover it to grow warmer with depth, reaching room temperature, or 70 degrees F (21 degrees C), at an altitude where the atmospheric pressure is about 10 times as great as it is on Earth. Scientists have conjectured that if Jupiter has any form of life, it might dwell at this level, and would have to be airborne. However, researchers have found no evidence for life on Jupiter. Additional reporting by Nola Taylor Redd, Space.com Contributor Explore the solar system Space Today Online - Moons of the Solar System SPACE TODAY ONLINE ~~ COVERING SPACE FROM EARTH TO THE EDGE OF THE UNIVERSE Moons of the Solar System Massive planet Jupiter below the moon Io click NASA image to enlarge A moon is a natural satellite rotating around a planet. While moons vary in size, each moon is much smaller than its planet. Almost 140 moons are known in the Solar System. Several moons are larger than the planet Pluto and two moons are larger than the planet Mercury. There also are many small moons that may be asteroids captured by their planets. Only Mercury and Venus do not have any moons.

By comparison, Earth has one moon and Mars has two. Jupiter has the most of any planet. Saturn is second. Pictures taken by the Hubble Space Telescope suggest there may be even more moons around those outer planets. earth's moon » Largest. The largest moon is Ganymede with a diameter of 3,280 miles, even larger than either of the planets Mercury and Pluto. Saturn's moon Titan is the second largest in the Solar System with a diameter of 3,200 miles, half again as large as Earth's Moon.

The Planets and Their Moons PLANET Jupiter 62 Io, Europa, Ganymede, Callisto, Amalthea, Himalia, Elara, Pasiphae, Sinope, Lysithea, Carme, Ananke, Leda, Metis, Adrastea, Thebe, Callirrhoe, Themisto, Kalyke, Iocaste, Erinome, Harpalyke, Isonoe, Praxidike, Megaclite, Taygete, Chaldene, Autonoe, Thyone, Hermippe, Eurydome, Sponde, Pasithee, Euanthe, Kale, Orthosie, Euporie, Aitne, plus others yet to receive names Saturn 33 Titan, Rhea, Iapetus, Dione, Tethys, Enceladus, Mimas, Hyperion, Prometheus, Pandora, Phoebe, Janus, Epimetheus, Helene, Telesto, Calypso, Atlas, Pan, Ymir, Paaliaq, Siarnaq, Tarvos, Kiviuq, Ijiraq, Thrym, Skadi, Mundilfari,

 Erriapo, Albiorix, Suttung, plus others yet to receive names Uranus 27 Cordelia, Ophelia, Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind, Belinda, Puck, Miranda, Ariel, Umbriel, Titania, Oberon, Caliban, Sycorax, Prospero, Setebos, Stephano, Trinculo, plus others yet to receive names Neptune Triton, Nereid, Naiad, Thalassa, Despina, Galatea, Larissa, Proteus, plus others yet to receive names Pluto 139 Saturn.

When the Cassini spacecraft from Earth arrived at Saturn in 2004, it promptly found two previously unseen moons. They turned out to be the smallest bodies seen until then around the ringed planet. The tiny natural satellites are about 2 miles and 2.5 miles in diameter. That's smaller than the city of Boulder, Colorado. Previously, the smallest moons seen around Saturn were are about 12 miles across. The moons are 120,000 miles and 131,000 miles from the center of planet Saturn between the moons Mimas and Enceladus. The newly discovered bodies were labeled S/2004 S1 and S/2004 S2. Later, they will be given names. The NASA JPL team wondered if S/2004 S1 might not be an object called S/1981 S14 that had turned up in a 1981 Voyager image. Saturn moons » Smallest.

The smallest moon is Deimos, at Mars, only seven miles in diameter, although its size now is rivaled by the small shepherd moons discovered by Cassini at Saturn and by others yet to be counted and named in the rings around Jupiter, Saturn and other giant gas planets in the outer Solar System. There may be tiny moons as small as only around a mile across. Pluto. Charon is the moon closest in size to its planet, Pluto. Earth's Moon is second in that comparison. Neptune. The interplanetary probe Voyager 2 in 1989 found six previously-unknown moons orbiting Neptune. They ranged in diameter from 33 miles to 250 miles. In 1991, they were named Naiad, Thalassa, Despina, Galatea, Larissa, Proteus. The names Galatea and Larissa were controversial since asteroids previously had been given those names. Names are assigned by the nomenclature committee of the International Astronomical Union (IAU). Triton. Before Voyager 2, astronomers knew Neptune had two moons, Triton and Nereid.

With a surface temperature of –391 degrees, Triton was found by Voyager 2 to have a thin veneer of methane and nitrogen on top of water ice on its surface. Triton had been thought to have a diameter of 2,361 miles, close in size to Earth's Moon, but turned out to be smaller, around 1,690 miles. Nereid is 210 miles in diameter. Pan. A new moon only 12 miles in diameter was discovered in 1990 circling the planet Saturn. It was Saturn's 18th and most distant moon. Photos of the planet, moons and rings, left over from the 1981 Saturn flyby by Voyager 2, had been filed away at NASA's Ames Research Center in Mountain View, California, for a decade. A planetary scientist was tipped off to Pan's presence by a disturbance in a 200-mi.-wide gap — Encke's Gap — in Saturn's outermost A ring. Pan's gravity moved particles in the large A ring, creating a gap with waves along the edges like the wake of a motorboat.

Checking the wavy edges, he calculated the probable position and mass of the moon and compared them with Voyager 2 positions and camera angles in 1980-81. When finally uncovered, the moon stood out as a small bright spot in 11 pictures among 30,000 photos scanned by a computer. In 1991, the moon officially was named Pan. It was the second time since Neptune was discovered in 1894 that a gravity disturbance had been used to pinpoint a previously-unknown Solar System body. Inner Solar System. The inner Solar System includes the planets Mercury, Venus, Earth and Mars. Of all the known moons in our Solar System, only three are in the inner region. Mars has two. Earth has one. Mercury and Venus are the only planets without moons. The outer Solar System includes Jupiter, Saturn, Uranus, Neptune and Pluto and the rest of the moons. More moons are discovered each year in the outer Solar System by astronomers using ever more powerful equipment. Atmospheres. Most moons are airless, but Jupiter's Io, Saturn's Titan and Neptune's Triton seem to have atmospheres. Titan may be flooded with an ocean of liquid ethane.

Triton may be covered by an ocean of liquid nitrogen. Io seems to have a thin sulphur dioxide atmosphere from volcanos. Titan. Titan appears to have an organic chemistry in its atmosphere which may resemble the primitive Earth before the dawn of life. It is the only moon known to have a thick, organic-rich nitrogen atmosphere. Surface temperature is around –290 degrees Fahrenheit. Solar System's moons are listed below: Exploring the Moons of the Outer Solar System The moons of the outer planets are popular targets with planners of future spaceflights. Jupiter has more moons than any other planet. Its best known moons are the four large planet-sized bodies Io, Europa, Ganymede and Callisto. jupiter » Callisto is the outermost of the four and the most heavily cratered body in the Solar System. It may have a vast water ocean indside. Io is innermost of the four. This sulfurous moon is the most volcanic world in our Solar System. It is peppered with hundreds of volcanoes, several of which might be active at any given moment. Europa has an icy surface that may hide a layer of warm slush or even liquid water.

That would make it one of the few places in the Solar System with that life-sustaining liquid. Ganymede is the largest moon of Jupiter and the largest moon in the Solar System. In fact, Ganymede is larger in diameter than the planet Mercury and much larger than the planet Pluto. Ganymede has its own magnetic field. Saturn has some unique moons. Here are some examples: Titan is Saturn's largest moon. Mimas has an enormous crater – probably a hole caused by a meteorite. Enceladus has a very bright surface. It may have active water volcanoes. Tethys has a canyon running three-quarters of the way around its surface. That means it may once have been split almost in half. Dione and Rhea have wispy white markings on one side. Hyperion is oddly shaped and the length of its day is constantly changing. Iapetus is half bright and half dark. Pan, by comparison, is a very tiny moon. Its diameter is only 20 km, which on the sale above would be only half the size of a BB. Uranus' moons are eye-openers. They have statuesque mountains towering more than ten miles high. Incredibly deep valleys.

Vast plains, some with a mysterious dark surface. Moon diameters range from a bit fatter than 25 miles up to about 1,100 miles. News | Largest Solar System Moon Detailed in Geologic Map News | February 12, 2014 Largest Solar System Moon Detailed in Geologic Map More than 400 years after its discovery by astronomer Galileo Galilei, the largest moon in the solar system - Jupiter's moon Ganymede - has finally claimed a spot on the map. A group of scientists led by Geoffrey Collins of Wheaton College has produced the first global geologic map of Ganymede, Jupiter's seventh moon. The map combines the best images obtained during flybys conducted by NASA's Voyager 1 and 2 spacecraft (1979) and Galileo orbiter (1995 to 2003) and is now published by the U. S. Geological Survey as a global map. It technically illustrates the varied geologic character of Ganymede's surface and is the first global, geologic map of this icy, outer-planet moon. The geologic map of Ganymede is available for download at: ).

"This map illustrates the incredible variety of geological features on Ganymede and helps to make order from the apparent chaos of its complex surface," said Robert Pappalardo of NASA's Jet Propulsion Laboratory in Pasadena, Calif. "This map is helping planetary scientists to decipher the evolution of this icy world and will aid in upcoming spacecraft observations." The European Space Agency's Jupiter Icy Moons Explorer mission is slated to be orbiting Ganymede around 2032. NASA is contributing a U.S.-led instrument and hardware for two European-led instruments for the mission. Since its discovery in January 1610, Ganymede has been the focus of repeated observation, first by Earth-based telescopes, and later by the flyby missions and spacecraft orbiting Jupiter. These studies depict a complex, icy world whose surface is characterized by the striking contrast between its two major terrain types: the dark, very old, highly cratered regions, and the lighter, somewhat younger (but still very old) regions marked with an extensive array of grooves and ridges.

According to the scientists who have constructed this map, three major geologic periods have been identified for Ganymede that involve the dominance of impact cratering, then tectonic upheaval, followed by a decline in geologic activity. The map, which illustrates surface features, such as furrows, grooves and impact craters, allows scientists to decipher distinct geologic time periods for an object in the outer solar system for the first time. "The highly detailed, colorful map confirmed a number of outstanding scientific hypotheses regarding Ganymede's geologic history, and also disproved others," said Baerbel Lucchitta, scientist emeritus at the U.S. Geological Survey in Flagstaff, Ariz., who has been involved with geologic mapping of Ganymede since 1980. "For example, the more detailed Galileo images showed that cryovolcanism, or the creation of volcanoes that erupt water and ice, is very rare on Ganymede." The Ganymede global geologic map will enable researchers to compare the geologic characters of other icy satellite moons, because almost any type of feature that is found on other icy satellites has a similar feature somewhere on Ganymede.

"The surface of Ganymede is more than half as large as all the land area on Earth, so there is a wide diversity of locations to choose from," Collins said. "Ganymede also shows features that are ancient alongside much more recently formed features, adding historical diversity in addition to geographic diversity." Amateur astronomers can observe Ganymede (with binoculars) in the evening sky this month, as Jupiter is in opposition and easily visible. The project was funded by NASA through its Outer Planets Research and Planetary Geology and Geophysics Programs. NASA's Jet Propulsion Laboratory is managed by the California Institute of Technology, Pasadena. News Media Contact

Question: Which is the largest moon in the solar system?
Answer: Ganymede